This invention pertains to a catalytic two-stage coal hydrogenation and liquefaction process for producing hydrocarbon liquid products having low nitrogen content, and in which the first stage catalytic reaction utilizes low coal space velocity which is significantly less than that for the second stage catalytic reaction.
Catalytic two-stage hydrogenation and liquefaction of coal to produce hydrocarbon liquid products is known, such as disclosed by U.S. Pat. Nos. 3,679,573 and 3,700,584 to Johnson; U.S. Pat. No. 4,111,788 to Chervenak et al; U.S. Pat. No. 4,842,719 and U.S. Pat. No. 4,874,506 to MacArthur, et al; and U.S. Pat. No. 4,816,141 to McLean et al. Although these processes provide high percentage conversion of both bituminous and sub-bituminous coals to produce low-boiling hydrocarbon liquid products, they provide only limited removal of undesired nitrogen compounds from the coal-derived liquid products. Such removal of nitrogen compounds from coal-derived liquids is quite desirable for environmental reasons. For known coal liquefaction processes, the conventional understanding has been that oxygen and sulfur are more susceptible for removal from the coal feed and liquid products than nitrogen. It has been theorized that the nitrogen in coal is tightly bound as pyridine, anilene and pyrollic compounds, and cannot be readily removed by known processes, whereas the oxygen in coal is removed as phenols, hydroxyls and ethers and the sulfur is removed as sulfoxides, thiophene and thiolether which can be readily treated.
Such problems with nitrogen removal from coal during liquefaction have now been substantially overcome by the present invention. It has now been unexpectedly discovered that removal of nitrogen compounds from coal and coal-derived liquid products is enhanced by use of critical low space velocity reaction temperature and catalyst characteristics in the first stage reactor of a multi-stage coal liquefaction process, as provided by a larger volume for the catalytic first stage reactor as compared to the second stage reactor.